linux-kernel - Re: [PATCH 0/3] remove rw_page() from brd, pmem and btt

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Date:   Fri, 28 Jul 2017 10:31:43 -0700
From:   Matthew Wilcox <willy@...radead.org>
To:     Ross Zwisler <ross.zwisler@...ux.intel.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org, "karam . lee" <karam.lee@....com>,
        Minchan Kim <minchan@...nel.org>,
        Jerome Marchand <jmarchan@...hat.com>,
        Nitin Gupta <ngupta@...are.org>, seungho1.park@....com,
        Christoph Hellwig <hch@....de>,
        Dan Williams <dan.j.williams@...el.com>,
        Dave Chinner <david@...morbit.com>, Jan Kara <jack@...e.cz>,
        Jens Axboe <axboe@...nel.dk>,
        Vishal Verma <vishal.l.verma@...el.com>,
        linux-nvdimm@...ts.01.org
Subject: Re: [PATCH 0/3] remove rw_page() from brd, pmem and btt

On Fri, Jul 28, 2017 at 10:56:01AM -0600, Ross Zwisler wrote:
> Dan Williams and Christoph Hellwig have recently expressed doubt about
> whether the rw_page() interface made sense for synchronous memory drivers
> [1][2].  It's unclear whether this interface has any performance benefit
> for these drivers, but as we continue to fix bugs it is clear that it does
> have a maintenance burden.  This series removes the rw_page()
> implementations in brd, pmem and btt to relieve this burden.

Why don't you measure whether it has performance benefits?  I don't
understand why zram would see performance benefits and not other drivers.
If it's going to be removed, then the whole interface should be removed,
not just have the implementations removed from some drivers.